Hormone receptors in the brain, particularly the estrogen receptor, have been shown to play a major role in the development and maintenance of sex differences in behavior. However, the role of the androgen receptor in this process is less understood. Therefore I propose to investigate the role of the androgen receptor in two types of behavior, sensorimotor gating and anxiety, using male mice and rats with the testicular feminization mutation (TFM), a mutation in the androgen receptor gene that renders the protein nonfunctional. Experiment 1 will test the hypothesis that the androgen receptor is involved in the regulation of sensorimotor gating and anxiety-related behaviors in adulthood by comparing behavior between TFM males, wild type males and wild type females. Since TFM male mice and rats have different circulating testosterone (T) levels than their wild type siblings, in Experiment 2 all animals will be gonadectomized, administered T, and tested for the same behaviors to reveal whether circulating T is acting on AR in adulthood to affect behavior. Experiment 3 will test whether differences in sensorimotor gating and anxiety in adulthood are the result of androgen induced organization during development.